CCNP MPLS and VPN Technologies 2 — Questions and Answers
Question 1: What is a Route Target (RT) used for in MPLS L3VPN?
- To assign MPLS labels to VPN prefixes in the LFIB
- To control which VRFs import and export routes between PE routers (Correct answer)
- To define the BGP AS path for VPN routes
- To set the QoS DSCP value on VPN-labeled packets
Correct answer: To control which VRFs import and export routes between PE routers
Route Targets are BGP extended communities attached to VPNv4 prefixes; a VRF exports RTs with sent prefixes and imports prefixes that carry matching RTs, controlling inter-VPN connectivity.
Question 2: In MPLS TE, which protocol is used to signal and establish label-switched paths (LSPs)?
- LDP
- RSVP-TE (Correct answer)
- BGP with TE extensions
- OSPF-TE
Correct answer: RSVP-TE
RSVP-TE (Resource Reservation Protocol - Traffic Engineering) is the signaling protocol used to establish MPLS-TE tunnels, reserving bandwidth and specifying explicit paths.
Question 3: What is the role of CSPF (Constrained Shortest Path First) in MPLS Traffic Engineering?
- It replaces IS-IS/OSPF as the IGP for TE-enabled networks
- It computes an explicit path for a TE tunnel that satisfies bandwidth and constraint requirements (Correct answer)
- It balances traffic across equal-cost multipaths in the LFIB
- It redistributes TE tunnel metrics into the BGP table
Correct answer: It computes an explicit path for a TE tunnel that satisfies bandwidth and constraint requirements
CSPF uses the Traffic Engineering Database (TED) populated by IGP extensions to compute a constrained path for TE tunnels that meets bandwidth, affinity, and other user-defined constraints.
Question 4: Which MPLS VPN model allows two VPNs to share specific routes, such as a shared services VPN?
- Hub-and-spoke VPN
- Extranet VPN using overlapping RTs (Correct answer)
- Full-mesh VPN with unique RDs
- VPLS with H-VPLS hierarchy
Correct answer: Extranet VPN using overlapping RTs
An extranet configuration imports Route Targets from a shared-services VRF into customer VRFs, allowing selective route leaking between otherwise isolated VPNs.
Question 5: What does the 'ip vrf forwarding' command do when applied to a router interface?
- Enables MPLS label imposition on the interface
- Associates the interface with a specific VRF, removing it from the global routing table (Correct answer)
- Activates LDP neighbor discovery on the interface
- Configures the interface as a VPN inter-AS link
Correct answer: Associates the interface with a specific VRF, removing it from the global routing table
Applying 'ip vrf forwarding <vrf-name>' to an interface binds it to that VRF's routing table, removing any previously configured IP address (which must be reconfigured).
Question 6: In MPLS L3VPN Option B inter-AS connectivity, what is exchanged between the ASBR routers?
- VPNv4 routes with original next-hop preserved via BGP next-hop unchanged
- Labeled VPNv4 routes with next-hop changed to the ASBR's own address (Correct answer)
- Unlabeled IPv4 prefixes redistributed into the remote AS IGP
- GRE tunnels carrying full VRF routing tables between ASBRs
Correct answer: Labeled VPNv4 routes with next-hop changed to the ASBR's own address
In Option B, ASBRs exchange labeled VPNv4 routes via eBGP and set themselves as the BGP next-hop, so the remote PE allocates a label for the ASBR and the ASBR stitches the label to the VPN label.
Question 7: Which command on a Cisco PE router verifies that a VRF has the correct Route Distinguisher and Route Targets configured?
- show ip bgp vpnv4 all
- show vrf detail (Correct answer)
- show mpls ldp neighbor detail
- show ip vrf interfaces
Correct answer: show vrf detail
'show vrf detail' displays the VRF's RD, import/export Route Targets, associated interfaces, and address families configured on the PE router.
CCNP MPLS and VPN Technologies 2
What is a Route Target (RT) used for in MPLS L3VPN?